Three primary types of bicycle trainers or exercise devices are known in the prior art. In "roller" type trainers, the rear wheel of a two-wheeled bicycle is supported on two parallel rollers. As a user pedals, the rear wheel rotates, causing the rollers to rotate. The rolling friction of the bicycle tire against the rollers simulates the actual rolling resistance that a bicycle rider would have to overcome while peddling the bicycle at the same speed on a level road. Such bicycle trainers cannot simulate wind resistance or resistance caused by varying terrain.
A second type of trainer that overcomes some of the limitations of "roller" type trainers is commonly known as a "wind trainer." Wind trainers include a fan assembly that is placed in rotational contact with the rear wheel of a bicycle. As the rear wheel rotates, the fan assembly rotates and generates a load that is proportional to the load that would be produced by wind resistance if the pedalist were actually riding the bike on the road at the same speed. Most wind trainers include a frame in which to mount the bicycle such that the fan assembly is positioned beneath the rear wheel of the bicycle and is frictionally engaged by the rear wheel.
Although wind trainers represent a significant improvement in bicycle training devices, they have a number of limitations. Wind trainers provide increasing resistance to the bicyclist as the rear wheel, and thus fan assembly, rotate at increasing speeds. However, wind trainers do not simulate the varying resistances produced during actual riding over varying terrain, up or down hills, etc.
To improve upon prior roller-type trainers and wind trainers, a third type of training device has achieved widespread use during the past several years. This new class of trainers, termed "eddy current" trainers, include an eddy current brake that is rotationally coupled to the rear wheel of the bicycle. The eddy current brake includes a shaft that is placed in rotational contact with the rear wheel of the bicycle. As the rear wheel of the bicycle rotates, it rotationally drives the shaft.
In one prior eddy current brake, a plurality of permanent magnets are arranged on both sides of the conductive disk. As the disk rotates, the permanent magnet's magnetic fields induce eddy currents within the rotating disk. The eddy currents in turn produce electromagnetic fields that interact with the permanent magnet's magnetic fields. This interaction of electromagnetic fields produces a resistance to the rotation of the disk, and thus the shaft and rear wheel of the bicycle. The amount of torque produced by the eddy current brake is influenced by a number of factors, including the size and shape of the permanent magnets, the placement of the permanent magnets around the rotating disk, the size and thickness of the rotating disk, the material out of which the rotating disk is formed, the spacing between the disk and magnets, and the speed at which the disk rotates, to name a few.
The faster the bicyclist pedals, the faster the resulting rotation of the rear wheel and disk, and thus the greater resistance produced by the eddy current brake. In some eddy current type trainers, the bicyclist cannot alter the configuration of the eddy current brake. In these trainers, the resistance changes as a function of the rate at which the rear wheel of the bicycle rotates. Such eddy current trainers are not capable of simulating actual bicycling conditions, such as changing elevations due to hills, etc.
Other eddy current trainers allow the bicyclist to alter the configuration of the permanent magnets during use. This type of trainer thus gives the bicyclist a means in addition to changing the rate at which the rear wheel rotates for altering the resistance of the eddy current brake. However, such trainers are still highly limited in their ability to simulate the wide range of resistances experienced during bicycling on the open road.
A more recent improvement upon eddy current trainers is the incorporation of eddy current brakes that use electromagnets, as opposed to permanent magnets. The use of electromagnets allows individual or groups of magnets to be energized at specified times and voltages to produce variable torques, and resistances to the rotation of the bicycle's rear wheel. The use of electromagnets allows the resistance or braking force to be set to any desired level or varied in order to duplicate actual road conditions experienced by a bicycle rider. Trainers incorporating such eddy current brakes can take into account wind resistance, head winds, changes in elevation, rider inertia, rolling resistance, the effects of drafting, etc. An eddy current trainer that uses electromagnets to simulate real life bicycling road conditions is sold under the trademark COMPUTRAINER.RTM. by Racermate, located at 3016 N.E. Blakely Street, Seattle, Wash. 98105.
Although the use of electromagnets in eddy current bicycle trainers has dramatically improved the trainers, there are still some limitations. During use in high-end or professional applications, it has been discovered that certain factors may cause unwanted variations in the torque and resistance produced by eddy current bicycle trainers varies during use. For example, temperature changes in the eddy current disks have been shown to cause variations in the torque and resistance. The load or resistance produced by the eddy current trainer is one of the variables used to measure the energy expended, and thus physical performance of the user. It is important, particularly in professional athletic training, to obtain an accurate measurement of the athlete's energy output in order to identify areas in need of improvement. However, in past eddy current trainers, the torque, and thus measured athlete's energy output, may change between measurements, even if the athlete's output actually remains constant. Thus, it is not currently possible to use eddy current trainers to obtain highly accurate measurements of an athlete's performance.
As can be seen from the above, there exists a need for eddy current exercise trainers that produce accurate and consistent torque/resistance measurements during sustained use. The present invention is an improved eddy current exercise trainer directed to fulfilling this need.